1. Field of the Invention
The invention relates to a method of manufacturing a semiconductor device and, more particularly, to a method of forming a bonding pad.
2. Related Background Art
FIGS. 1 and 2 are respectively a cross sectional view and a plan view showing a state in which a protecting film is formed on a bonding pad portion by a conventional method.
Reference numeral 1 denotes a semiconductor substrate; 2 a wiring; 3 an insulating layer; 4 an opening portion; and 4' a contact hole.
To date there is a method of manufacturing a monolithic IC as a device in which a number of active elements such as transistors and a number of passive elements such as resistors are formed on the same substrate and wirings among those elements are connected and one circuit or system is constructed. According to such a conventional manufacturing method, the Al or Al alloy wiring 2 having a thickness of about 0.8 to 1.6 .mu.m is formed on the substrate 1 by a sputtering method, thereby forming a desired pattern by a photolithography step. The pattern formed as mentioned above is generally patterned so as to include an electrode portion for lead connection, namely, a bonding pad having a size of about 50 to 100 square .mu.m in order to lead out a signal from the device to the outside. An SiN film as a protecting film 3 is subsequently formed by a plasma CVD method and a bonding pad portion is opened.
A thin metal wire 14 of Al or Au is bonded to the opening portion 4 and is connected to an external terminal 15 of the package. In the case of TAB (tape automatic bonding), after the bonding pad portion was opened, a contact barrier layer as an Au layer having a thickness of about 1000 to 2000 .ANG. and a thick resist layer are coated and the resist on the bonding pad is eliminated by development. After that, an Au film of a thickness of about 25 .mu.m is formed by an electro-plating and the resist and the contact barrier layer are eliminated, thereby forming a bump. After that, a tape bonding is performed.
In the above conventional method, it is desirable to set a film thickness of the wiring of the bonding pad portion to a value of 0.6 .mu.m or more from a viewpoint of an adhesion strength with the bonding wire. That is, when the film thickness of wiring metal of the bonding pad portion is thick, the pad portion is softly deformed upon bonding, so that an enough adhesion strength is obtained. However, due to the improvement of an integration degree of the IC and the realization of an advanced function, the bonding pad portion cannot always satisfy the condition as mentioned above. For instance, as for the film thickness of wiring, it is inevitable to make the film thin in order to reduce the line width and the pitch between lines. As for the wiring material, a metal of a high melting point such as W, Mo, Ti, or the like or its silicide is used in place of the conventional Al or Al alloy, so that a large problem occurs for the adhesion strength.
On the other hand, there are problems such an in the case of forming the bump, the formation of the contact barrier layer and the electro-plating are necessary and a processing time is long, and in the eliminating step of the contact barrier layer, there is a possibility of the occurrence of a defect in the protecting film, and the like.